gonext migrate CLI subcommands

[tayebmokni]

Summary

Wire gonext migrate CLI subcommands per doc 08 §3.1, §15. Subcommands: discover, plan, preview, execute, verify, rollback. Each is a thin client over the same Go API the admin UI calls; both surfaces use the same Asynq queue. CLI is required for sites > 100k posts, headless/CI integrations, and resuming long-running migrations from a different machine.

Design reference

• docs/08-migration-compat.md §3.1 (CLI commands), §15

Acceptance criteria

• gonext migrate discover [--from-wpdb ... | --from-wxr ... | --from-rest ...]
• gonext migrate plan --source <id> writes migration-plan.json
• gonext migrate preview --plan <path> (dry-run on sample)
• gonext migrate execute --plan <path> [--resume]
• gonext migrate verify --plan <path>
• gonext migrate rollback --to-snapshot <id>
• All commands stream progress (SSE → terminal progress bar)
• --json flag for machine-readable output
• --help documentation per subcommand
• Auth: same token mechanism as other CLI commands

Dependencies

#importer-scaffold

Complexity

M

[tayebmokni]

Closing — shipped in the final-wave PR (#487-#492). Auto-close only fires for first ref.